1. Field of the Invention
The present invention relates to a projection tube which is used in a projection type TV receiver, a video projector or the like.
2. Description of the Related Art
An image may be created by scanning an electron beam emitted from an electron gun onto a cathode ray tube via a deflection yoke. The deflection yoke is mounted near a joint portion, which is located between a neck and a funnel. The deflection sensitivity of the deflection yoke is increased when the outer diameter of the neck is decreased. However, when the outer diameter of the neck is decreased in order to enhance the deflection sensitivity, the electron gun which is accommodated in the neck portion must be miniaturized correspondingly. When the electron gun is miniaturized, the diameter of an electron lens of the electron gun is decreased and hence, focusing is degraded. Therefore, it can be seen from the above description that increasing the deflection sensitivity by decreasing the outer diameter of the neck may result in decreased focusing performance.
A method which can solve such a problem is, for example, proposed in U.S. Pat. No. 3,163,794, which discloses a technique for enhancing the deflection sensitivity by making the outer diameter of a neck portion on which a deflection yoke is mounted smaller than the outer diameter of a neck portion in which an electron gun is accommodated. The maximum operating voltage of the cathode ray tube described in this patent is set to 16 kV.
On the other hand, with respect to a color cathode ray tube, Japanese Laid-open Patent Publication 185660/1999, discloses a technique for enhancing the deflection sensitivity by making the outer diameter of a portion of a neck on which a deflection yoke is mounted smaller than of a portion of the neck in which an electron gun is accommodated.